애를 써요 · 애를 썼어요 · 애쓰셨어요 (ㅡ drops)
to make a great effort, to try hard
Example
잊으려고 애를 썼지만 쉽지 않았어요.
I tried hard to forget, but it wasn't easy.
Word parts
애 here means 'anxious effort,' a homonym of 애 'kid.'
Good to know
애쓰셨어요 is a warm way to thank someone for their hard work.